How did excavated clay molds help date the creation of the Statue of Zeus?

Excavations conducted between 1954 and 1958 at the site of a building identified as the "workshop of Phidias" at Olympia provided the evidence needed to date the Statue of Zeus.

Archaeologists discovered a large quantity of waste material within the workshop, including tools, ivory fragments, and heavy terra-cotta molds used for shaping the gold sheets of the statue's drapery. Crucially, the debris contained pottery that allowed researchers to date the activity of the workshop to the years around 430 BCE. This discovery settled a long-standing historical debate regarding whether the Olympian Zeus was created before or after Phidias’s other major work, the Athena Parthenos, which was dedicated in 438 BCE. The findings confirmed that the statue was produced during the later period of the sculptor's life.123